Alloy



Patented Jan. 15, 1929.

UNITED STATES PATENT OFFICE.

PM O. CHESTERFIELD, OI DETROIT, MICHIGAN, ASSIGNOR T CHESTERFIELD METALCOMPANY, OF DETROIT, MICHIGAN, A CORPORATION 01" MICHIGAN.

ALLOY.

Il'o Drawing.

This invention relates to alloys, more particularly those designed foruse in the production of high speed cutting tools.

This application is a continuation in part 5 of. my ap lications SerialNo. 493,108, filed August 1 1921, and'Serial No. 628,801, filed March22, 1923. 1

It is necessary that alloys for such purposes have the property ofred-hardness so that a tool made therefrom may maintain its cutting edgeafter the same has become red hot.

In addition to heat resistance, the alloy must also possess abrasivehardness and for 16 this purpose should contain embedded 1n the metallicmatrix hard crystals, usually metallic carbides.

Alloys of this general character are known comprising cobalt, chromiumand k 20 tungsten. Both chromium and tungsten form carbides and of thesethe harder is tungsten carbide, so that the chef funct on of thetungsten is to give the alloy abrasive hardness.

While tungsten will give alloys abrasive hardness, the use of tungstenis attended with certain disadvantages not possessed by other metals.

Thus the melting point of tungsten is excessivel high being over 3000 C,so that alloys t ereof have to be made by dissolv ng the tungsten in theother molten constituents, like sugar dissolves in water, instead of bythe admixture and mingling of molten tungsten with the other moltenmetals.

This renders the roduction of a homogeneous alloy more ifiicult. Thetemperature of formation of an alloy havlng large roportions of tungstenis also higher than 1s required to produce alloys of more easily fusiblemetals.

Further, the very high specific, gravity of tungsten (18.7) as'comparedwith that of nickel or cobalt (8.7) or chromium (6.0)

tends to produce segregation of the constituents of the alloy andhinders the production of a homogeneous alloy.

Moreover, the amount of tun sten re quired to give the desired degree oiabrasive hardness is higher than those of certam other metals.

The object of the present invention, therefore, is to provide an alloycontaining a metal having the properties of nickel and I cobalt, and ametal capable'of forming a Application med Deoemcer 1, 1924. Serial No.753,354.

hard carbide and having a iower melting point than tungsten.

Another object of the invention is to provide an alloy in which thedesired abrasive hardness is produced by a smaller propor- 00 tlon ofthe hardening metal than is possible w1th tungsten.

Other and further important objects of the invention will hereinafterappear.

All of these three metals form hard carbides, thus titanium carbideis'harder than carborundum and will even scratch or score diamond.

These metals may be alloyed with cobalt and a small amount of carbonwithout substantial amounts of other metals. It is preferred, however,to employ either or both nickel and chromium in addition thereto.

While vanadium and chromium, for example, are similar in properties inso far as 7 they both form hard carbides, the hardening efi'ect ofvanadium is much greater than that of chromium. The latter metal has avalu able toughening effect so that to obtain the best results theindividual characteristics of these metals should be blended.

The same is true of nickel and cobalt. Alloys with nickel alone have atendency to be hot-short while the cobalt alloys tend to be cold-short.A combination of the two metals gives an alloy having the desiredtoughness and strength under all conditions.

The chief function of the cobalt and nickel appears to be that ofproducing a strong, tough, heat resisting matrix for the carbides of thechromium group or other group of metals. Neither cobalt or nickelpossess the affinity for carbon, that is possessed by chromium orvanadium for example, so that it is probable that there is little or nocarbide of either cobalt or nickel in my alloys.

The amount of carbon b weight in my alloys is comparatively slig t, say1.50%, but the proportion of carbide by volume may be over 10% oftheentire alloy. This follows from the great differences in specificgravity of carbon and the metals with which it combines to form carbide.In view of this large .content of non-metallic compounds, the INcomposition of the matrix is of great importance.

Ordinarily alloys made in accordance with this invention will consist ofcobalt, nickel, chromium and either. titanium, vana- 11o dium or niobiumwith a small amount of carbon.

The percentage of these metals will usually be within the followinglimits:

Percent. Cobalt 25 to Nickel 10 to 20 Chromium 25 to 40 Vanadium, etc 10to 25 The total amount of cobalt and nickel should be between 35 and Incertain cases a wider range of propors tions may be employed such asthose lying within the following percentages:

Per cent. Cobalt 15 to 55 Nickel 7 to' 30 Chromium 20 to 45 Vanadium,etc 4 to 30 The total amount of cobalt and nickel should be between 30and As an example of a suitable alloy falling within the above limitsthe following may be given:

' Percent. Cobalt 37 Nickel 15 Chromium 36 Vanadium, etc 12 If thecontent of nickel is increased there should be a corresponding increasein the vanadium to maintain the desired hardness. This is exemplified bythe following:

Percent. Cobalt 21 Nickel 28 Chromium 25 Vanadium 26 In some alloys thechromium may be omitted-thus Per cent.

Cobalt 40 Nickel 30 Vanadium 30 Further it may be found desirable to useonlyl'l cobalt and vanadium as in the following a oy:

Cobalt if??? Vanadium 25 p the metals forming the alloy, the latter oncooling will not contain free carbide crystals but only carbide in solidsolution.

While carbide in solid solution has a hardening effect it is not thedesired abrasive hardness which results from the presence of freecarbide crystals. The carbon content of the alloy should, therefore, behigh enough to provide a substantial proportion of free carbide crystalsin'the alloy.

If the carbon is too hi h the alloy will contain in addition to carbidefrce uncombined carbon in graphitic form. As a given amount of carbonwill combine with different weights of different metals to form ourhidesthe amount of carbon which may be added before free graphitic carbon isformed in the alloy will depend upon the nature and proportions of themetals composing the al- 10 llsually the amount of carbon in the alloywill be between 1 and 2.5%, for example around 1.5%, although in somecases it may be as low as 0.5 or as high as 3.5%. It ,is desirable onthe one hand to have enough carbon to produce free carbide crystals andon the other hand not enough to cause the formation of particles ofgraphitic carbon throughout the alloy, as the presence of graphlticcarbon greatly reduces the strength of the alloy.

The carbon is most readily and accurately added as a carbide, such asthe carbide of one of the metals forming the alloy as chromium.

In addition to a hardening element it is frequently advisable to use ade-oxidizer such as aluminum or boron. Further, the

hardening element and de-oxidizer may to advanta e be addedsimultaneously in the form ofioron carbide.

While my alloys consist essentially of the above metallic andnon-metallic .in edients it will be understood that the ad ition orpresence as impurities of small quantities of other metals, etc., suchas iron, manganese or the like, will not change the generalcharacteristics of m alloys.

In the process 0 forming the alloy the several ingredients in properproportion are placed in a crucible preferabl together with some readilyfusible materia such as glass, which will form a protecting layer overthe alloy and so prevent oxidation.

The temperature employed for fusing the constituents may be from 1750 to1950 C., according to conditions. As these alloys do not respond to heattreatment, as does steel, at least at a temperature below 1100 C., thealloy must be formed into the desired sha e by casting and then grindinginstead of by forging;

To 0 tain the best results molds made of sand should not be employedsince, such molds, even if brushed over with graphite owder, the barsare apt to be full of blow oles and too soft to make good lathe tools.Preferably the molds are conusing structed of graphite although castiron may be used for th1s purpose 1f the surface is treated before useto prevent the hot metal adhering thereto. Such treatment may consisteither in treatment with sulphuric acid or coating with carbon by theapplication of a smok flame thereto.

Grap ite is, however, much superior to cast iron as a material formolds. In the first place it is much easier to machine graphite thancast iron so that molds for casting special sizes and shapes can be morereadily made. Then again, cast iron molds have to be repeatedly treatedwith sulphuric acid solution since the effect of the treatment soonwears off.

Further, cast iron molds, especially for small sizes of bars, chill themetal too rapidly. This chilling makesthe bars hard,

and, while hardness is a desideratum, it should be uniform throu houtthe bar and chilling makes the outer layers harder than the center.

Now graphite has a lower specific heat per unit volume and also a muchlower heat conductivity than cast iron. Consequently the rate ofabstraction of heat from the cooling metal is far less in the case ofgraphite than in the case of iron molds.

I have also found that the hardness of bars cast with the above alloysvary according to the rate at which they cool so that a small bar, whichnecessarily cools more rapidly than a large one, is, otherconditionsvbeing the same, harder. On the other hand, increasing thecarbon content of the alloy increases its hardness. It has further beenfound that heat treatment of the alloy after casting does notappreciably change its hardness so that the alloy may be termedself-hardening.

To secure the best results it is necessary to hit the happy mean betweentoo eat hardness, which means brittleness, an liability to flake orchip, and too little hardness, which means that a tool made therefromwill be too soft to cut for the desired length of-time or to cut hardmetals.

This I accomplish by the present invention by var ing the amount ofhardenin element, suc as boron carbide, added wit var ing dimensions ofthe bar to be cast.

or exam 1e, for a inch bar 0.56% boron carbi 6 may be used to advantage;

. for a inch bar 0.85% and for a inch bar 0.97%.

By so varying the content of boron oarbide the sum of the hardness dueto chilling and the hardness due to the hardening element is maintainedsubstantially uniform irrespective of the size of the bar cast.

If on casting a trial bar from any given melt the alloy appears to betoo soft, small additions of tungsten may be added to the crucible togive the requisite hardness.

The above mentioned quantities of carbon, added as boron carbide, areconsiderably lower than the desired carbon contents of the bars for thereason that not only do the constituent commercial metals contain smallamounts of carbon but also larger amounts of carbon are icked up fromthe crucible in which the 1510 is made, if an unlined graphide cruciblee employed. i

As a result of the picklng u of carbon from the crucible it is desirab eto avoid heating the metal to too high a temperature or for too long atime 1n the crucible. Further, when remelting scrap along with aproportion of new metal the quantity of boron carbide added should bedecreased to allow for the carbon already in the scrap.

group capable of forming a hard carbide and havlng a melting pointbetween 1000 and 2100 C. with a small amount of carbon.

2. A high speed tool formed of a substantially non-ferrous alloycompring 15 to 55% cobalt, 7 to 30% nickel, 20 to 45% chromium and 4 to30% of a metal not in the chromium group capable of forming a hardcarbide and having a melting point between 1600 and 2100 C. with a smallamount ofcarbon.

3. An alloy for high speed tools com rising 25 to 50% cobalt, 10 to 20%nicke 25 to 40% chromium, 10 to 25% vanadium with a small amount ofcarbon.

4. An alloy for hi h ing approximately 3 cobalt, 15% nickel, 36%chromium, 12% vanadium with a small amount of carbon.

In testimony whereof I have hereunto subscribed my name.

PERCY c. CHESTERFIELD.

